‘on a Permanent Electric Current. 177 
This value is much nearer those obtained with the plates 4, 
5, and 6, but even now there is a discrepancy of eight or ten 
per cent. Without discussing this matter any further at pres- 
ent, I pass on to tell what has been observed with 
SILVER. 
Measurements have been made with four separate plates of 
this metal. The thickness of the strip was estimated in one 
case by weighing, in the three others by measuring the elec- 
trical resistance. I will give first the results obtained with the 
thick strip. . 
Silver Foil, No. 10. 
Length of strip when weighed = 7:98 cm 
Wiew - -< © ee 
Area including projections = 28. Mad 
Weight 047: 
.*. Thickness (taking sp. gr. to be 10°47) = += 000491 cm. 
With this plate 
MxV 
M. C. ’ 
Apr. 21st, 6580 kX tan 49° 17’ 114 x 10” 
¥ « eae 80 | ey 
Mean = 1160 x 10° 
Two of the other plates were prepared, not by fastening sil- 
ver leaf to glass with shellac, but by depositing from a solu- 
tion the silver directly upon the glass. The process made use 
of for this purpose was Béettger’s, as detailed in this Journal 
for 1867. The two plates were cut from the same piece o 
glass after coating. 
Silver Film (A). 
Length between the contact blocks = 6°05 em 
Width = 2°46 om. 
Electrical resistance, as measured, = 1:45 ohms. 
ened the rip by placing the blocks nearer together, then 
measured the length and again determined the resistance of the 
whole. This process was repeated, thus giving three values of 
the resistance corresponding to the three lengths of the strip 
employed. From these values the contact resistance is readily 
determined, though of course very roughly. It appeared to be 
equal to the resistance of about 27 cm. of the strip itself, and 
Am. Jour. epic" * anaes Vou, XX, No. 117.—Srprt., 1880, 
